People spend approximately 90% of their time indoors, a substantial amount of this at work, in an office.
White light sources can produce high quality light with a color rendering index above 90 with very high efficiencies. In general, compared with natural sunlight, such light sources do not have certain parts of the spectrum, such as the UV part of the electromagnetic spectrum.
However, natural sunlight, and the UV content in particular, is essential for the human body, for example for vitamin D production. It would therefore be desirable to have times during the working day when exposed to natural sunlight. This exposure for example would help the prevention of osteomalacia in adults. Studies have found that 90% of the population worldwide is below sufficient levels of Vitamin D, because of too limited exposure to sunlight, and in particular the UV component of natural sunlight, especially in winter time. A correlation between low vitamin D levels and the incidence of a large number of health issues has been identified, for example mood, energy, muscle weakness, cardiovascular disease, multiple sclerosis, diabetes, obesity, depression, Alzheimer's, cancers, etc.
More and more people want a better work-life balance, and would therefore appreciate exposure to more healthy lighting during the working day. In addition, increasing numbers of people take vitamin D supplements for the prevention of osteomalacia, because of the problem that artificial lighting does not enable sufficient synthesis of vitamin D.
However, it is not easy to provide natural sunlight in an office environment. There is therefore a need for a lighting system which is able to replicate the benefits of natural sunlight, but which can be used in an indoor environment, such as an office environment.
For this purpose, it is possible to introduce UV LEDs in combination with white LEDs and also colored light. Furthermore, the use of UV LEDs has also been proposed for producing both white light and also colored light.
Low intensity UV light may also be used for other applications such as for skin tanning, insect attraction, skin treatment, disinfection, etc. Thus, systems which provide UV light as well as visible light have applications other than for emulating natural daylight.
It is known that UV light tends to degrade many of the polymers which are used in current lighting applications, for example in a lighting diffuser.
There is therefore a need for a lighting system which enables the provision of UV lighting as well as visible lighting, but without degrading the polymers which are desired in the lighting system.